v.
When a white person claims to have 'discovered' something that already existed. Like Columbus did with the Americas. It usually entails taking credit for something that may be part of someone's culture and might already have been there, such as black fashion, African American slang, or twerking and dreadlocks.

Christopher Columbus is acclaimed for having 'discovered' the new world. Him, an European white guy backed by the Spanish crown just waltzed in and took over the land and the people who had been there for thousands of years with their culture and form of life. Him and his men brought illness and suffering and Christianity to the 'savages'.
A similar trend is seen when white, middle-class people move into neighborhoods that are predominantly non-white and of a lower socio-economic level and hype up the prices, kicking out the inhabitants who've lived there for generations. Gentrification is a form of Columbusing.

Whenever a white dude wear dreads, like most white people who don't know the cultural and religious implications of doing so, they are guilty of Columbusing.

When a non-white racist posts a definition on Urban Dictionary and uses his ignorance of post-Moor-invasion Spain to act as though he's being clever by ripping white people for claiming old shit as their own.

Dave: "Hey, bro- check out this ignorant definition in the Urban Dictionary-- this dude thinks Columbus was white and he's pretending that only white people claim old shit like they invented it."
Jamal: "Hang on, I gotta finish this beat I made out of an old Lynyrd Skynyrd sample for this album I'm burning so Rihanna can put her name on it... Oh, damn! Yeah, even I have to admit he's Columbusing that shit."